As mobile device technology continues to develop and demand therefor continues to increase, demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle lifespan, and a low self-discharge rate, are commercially available and widely used.
As cathode active materials for lithium secondary batteries, lithium-containing cobalt oxides such as LiCoO2 are mainly used. In addition thereto, use of lithium-containing manganese oxides such as LiMnO2 having a layered crystal structure, LiMn2O4 having a spinel crystal structure, and the like and lithium-containing nickel oxides such as LiNiO2 is also under consideration.
Among cathode active materials, LiCoO2 is widely used due to excellent overall physical properties such as excellent cycle properties, and the like. However, LiCoO2 is low in safety and expensive due to resource limitations of cobalt as a raw material. Meanwhile, lithium manganese oxides, such as LiMnO2, LiMn2O4, and the like, are advantageous in that they contain Mn that is abundant as a raw material and environmentally friendly and thus are drawing much attention as a cathode active material that can replace LiCoO2. However, such lithium manganese oxides have low capacity and poor cycle properties.
In addition, lithium nickel-based oxides such as LiNiO2 are less expensive than cobalt-based oxides and, when charged to 4.25 V, the lithium nickel-based oxides have high discharge capacity. Thus, reversible capacity of doped LiNiO2 approximates to 200 mAh/g, which exceeds the capacity of LiCoO2 (about 153 mAh/g). Accordingly, in spite of somewhat low average discharge voltage and volumetric density, commercially available batteries including LiNiO2 as a cathode active material have improved energy density and therefore research into these nickel-based cathode active materials has recently been underway in order to develop high-capacity batteries. However, problems of the nickel-based cathode active materials such as LiNiO2, such as high production costs, swelling due to gas generated by batteries, low chemical safety, high pH, and the like, remain unsolved.
Therefore, composite metal oxides have been proposed as an alternative. Among composite metal oxides, xLi2MO3*(1−x)LiMeO2, where M is at least one element selected from Mn, Zr, and Ti; and Me is at least one element selected from Ni, Co, Mn, Cr, Fe, V, Al, Mg, and Ti consists of a solid-solution complex of Li2MO3 and LiMeO2, and thus, may be stable at high voltage and have high discharge capacity. When such composite metal oxides are used in a general co-precipitation process, however, it is difficult to effectively synthesize a transition metal precursor used to prepare a composite metal oxide due to a high manganese content.
In spite of a variety of approaches as described above, a precursor for preparation of a lithium composite transition metal oxide which exhibits satisfactory performance and a lithium composite transition metal oxide including the same have not yet been developed.